A) Field of the Invention
This invention relates to a communication apparatus that has a dominated node and a dominating node, and more specifically, a dominating node that can manage other node and a dominated node that is managed by the dominating node.
B) Description of the Related Art
IEEE 1394 Standard published by the Institute of Electrical and Electronics Engineers is known as a serial bus interface standard which can execute a voluminous and rapid digital data transmission. An interface based on the IEEE 1394 Standard or a device equipped with the interface (hereinafter both are called the IEEE 1394 device) is equipped with an IEEE 1394 bus protocol formed of hardware (a lower layer) that forms one node and protocols (an upper layer) such as a device control, an isochronous transmission control, etc. by means of software placed over the lower layer.
FIG. 12 is a schematic block diagram showing an example of protocol stack of a general audio visual (AV) device equipped with the mLAN™ (trade-mark) upper layer. The mLAN standard is connection management technology relating to a music data digital network for music performance data and audio data, the technology using the IEEE 1394 Standard and is an application located in the upper application.
The lower layer is, for example, constituted of each layer of a physical layer, a link layer, a transaction layer and a serial bus management.
The physical layer regulates the physical interface and the electric interface and is generally made of hardware. In the link layer, a one-way transmission service called sub-action and a packet handler that is a packet transmission/reception service are provided. The link layer is also generally made of hardware as same as the physical layer. In the link layer, for example, services concerning to the asynchronous transmission and the isochronous transmission are provided.
Also, especially in the isochronous transmission, since a signal that needs a rapid process such as an audio signal, a video signal and the like is managed, all the services are provided in the link layer that is hardware.
The transaction layer executes a process concerning to the asynchronous transmission. The transaction is a data transmission of a request-response type. There are three transaction types, namely, a read transaction, a write transaction and a lock transaction.
The read transaction is a transaction used for reading data from a specific target address space. The write transaction is a transaction used for writing data in a specific target address space. The lock transaction is a transaction used for renewing data in a specific target address space in accordance with reference data.
The bus management is a module for intensively managing resources on the serial bus. The bus management includes management of power supplies, management of a topology map and a speed map, management of isochronous resources, and the like.
The upper layer is software for managing the lower layer and the whole node, and is constituted of, for example, the 1394AV protocols (IEC-61883) and mLAN upper layer.
The AV protocols define a common isochronous packet (CIP) format for expressing the data contents of an isochronous packet, a connection management protocol (CMP) for managing connections by defining a virtual “plug”, a function control protocol (FCP) for managing other devices connected to the IEEE 1394 bus, and the like.
The mLAN upper layer is a protocol layer for transmission of audio/music information in accordance with the IEEE 1394 standard. The mLAN upper layer is constituted of an audio/music information transmission protocol and a connection management protocol both complied with the 1394AV protocols.
The audio/music information transmission protocol is used for adding the format for transmitting audio/music information to the definition of CIP. The connection management protocol is used for performing autonomous connection management of each node by using an intelligent CMP.
All IEEE 1394 devices connected to an IEEE 1394 bus have the upper and lower layers although the functions thereof are different more or less.  @ @ The upper layer is more complicated than the lower layer. Therefore, hardware resources necessary for the upper layer increase more than the lower layer. The manufacture cost rises if the upper layer is used for all IEEE 1394 devices.
The upper layer is more relevant to a user interface than the lower layer. Therefore there are many chances of feeding back revision requests from users. Although it is desired that the upper layer has the structure easy to match a new specification, the manufacture cost rises if the structure of the upper layer of each of all IEEE 1394 devices is made easy to upgrade.
In a section of a preferred embodiment in Japanese Patent Application 2001-220895, the application being filed by the same applicant of the present application, it is suggested that other dominating node executes by proxy a function of the dominated node that does not have the upper layer. In the invention of Japanese Patent Application 2001-220895, a GUID of the dominating node to execute a function by proxy of the upper layer is written in a storage area of the dominated node. Therefore, a function of the dominated node can be used from other general node via the dominating node.
However, according to the above-described invention, when the dominating node that has the GUID written in the storage area does not response for some reason, other general node cannot use the dominated node.
Also, when the dominating node of a newer version participates in the network, and in the case that it is more effective for using the function of the dominated node when other dominating node executes it by proxy, other dominating node could not use the dominated node that is managed by other dominating node.